1. Field of the Invention
The present invention relates generally to systems and methods for the control of railroad crossing signals and devices. In other aspects, the invention relates to systems and methods for providing train location and travel information to remote locations and for tracking train traffic generally.
2. Description of the Related Art
Rail crossings, intersections where a railroad track crosses a roadway, have long presented a significant danger for vehicular traffic. Each year many car/train accidents occur at these locations.
There is a widespread belief that many such accidents result, directly or indirectly, from an inherent unreliability in the present "island circuit" arrangement used to actuate rail crossing safety devices. The island circuit system is an electromechanical system used to operate flashing crossing lights and crossing blocking arms. Functioning of this system is based upon the movement of a train into an "island circuit" which is located a short, predetermined distance around (i.e., on either side of) a railroad crossing. As the train passes over the island circuit, an electrical signal is generated indicative of the train's location within the "island" bounded by the predetermined distance. The signal is then transmitted along the track to a relay located near the railroad crossing. Upon receipt of the signal, the relay actuates flashing lights and lowers crossing blocking arms.
Unreliability in the island circuit system can cause rail crossing safety devices to be activated in error or even to fail to activate when necessary. Inadvertent activation occurs when salt, mud, water or other contaminants cause the island circuit system to shunt. It is believed by some that numerous such false alarms may lead to a conditioned disregard by some motorists of the crossing safety devices. On the other hand, the crossing devices can fail to activate due to contaminants, such as grease, that keep the train from completing the circuit. As a result, the signal indicating the presence of the train is not transmitted to the crossing.
Further, the warning time provided by island circuit systems is variable. Usually, the island circuit is configured so that safety devices adapted to govern vehicular traffic across a railway are activated when an approaching train is a certain distance from the rail crossing. These rail crossing safety devices include flashing lights and chimes as well as rail crossing blocking members or arms. Given the average speed of trains, this amount of time is on the order of twenty to thirty seconds warning before the train reaches the crossing and the crossing arms block the crossing. In actuality, however, trains may be either faster or slower than the planned average. Thus, the actual warning time varies based upon the actual speed of individual trains.
Some "constant warning time" systems are known which provide a predetermined amount of warning time regardless of the speed of an approaching train. These systems are complex electromechanical arrangements that measure the electrical resistance associated with passing trains and use the measurement to approximate the speed of the train. Variations in the train's speed are then compensated for so that, for a faster train, the safety devices at the crossing are activated earlier; for a slower train, the safety devices are activated slightly later.
A major drawback to both constant warning time systems and conventional island circuit systems is the expense associated with installing and maintaining these systems. Further, these arrangements provide only limited information to vehicle operators concerning the approaching train. Specifically, only the fact that a train is approaching the crossing is indicated.
A rail crossing collision avoidance system concept is discussed in U.S. Pat. No. 5,699,986 issued to Welk. This concept provides a general method whereby road vehicles in the vicinity of a rail crossing are informed of a train approaching the crossing. The patent discusses the use of data obtained from global positioning system (GPS) devices located on trains and/or at railroad crossings to provide such information. A processor/transmitter controller is located either on the train or at the train crossing itself to perform the calculations to determine train arrival times. If it is determined that an alarm condition exists, an alarm signal is transmitted to individual road vehicles which are equipped to receive it.
Another GPS-based rail crossing warning system is discussed in U.S. Pat. No. 5,554,982 issued to Shirkey et al. According to this patent, a GPS receiver is installed on top of a train and used to obtain information concerning the train's speed and position. This information is then transmitted to a rail crossing-based transceiver. When the train's estimated time of arrival at the crossing is within a predetermined range, the transceiver transmits the boundary coordinates of a warning zone. A road vehicle-based receiver receives the warning zone signal and the crossing's position. The receiver then determines the road vehicle's position and speed and produces an alarm to the road vehicle's operator when the vehicle is inside the warning zone and its distance to the crossing is within another predetermined range, which is a function of the road vehicle's speed.
The systems discussed in Welk and Shirkey et al. contain a number of disadvantages. First, they are useful to determine the position of only a single train in relation to a single railroad crossing. Thus, the system is not useful for deriving arrival time and train speed information for a number of different trains. Also, it is not possible to use them to derive information concerning the identity of individual trains. Further, centralized control and communications are not possible.
A system based upon the concepts discussed in the Welk and Shirkey et al. patents would also be expensive and perhaps impractical since specially-made receivers are needed in each individual road vehicle in order for the system to be fully operational. Because maintenance and upkeep of these receivers would undoubtedly be left to the discretion of the owners and operators of the individual road vehicles, the system might become unreliable.
In addition, it will be appreciated that the Welk and Sharkey et al. patents discuss only general concepts and do not reveal the structural and functional details of a controller which is capable of receiving a message and, in response thereto, controlling the safety features of a railroad crossing.
The present invention addresses the problems inherent in the prior art.